1. Field of the Invention:
The present invention relates to an insect pesticidal composition. More particularly, it relates to an insect pesticidal composition which controls pests for rice such as brown planthopper and sanitary pests at a small dose.
2. Description of Prior Arts:
As virus diseases on rice plants in Japan and South East Asia, dwarf, stripe, black-streaked dwarf and yellow dwarf, being medicated by green rice leafhopper and smaller brown planthopper, have been known and necrotic mosaic caused by a soil infection has been known.
Recently, breeding of grassy stunt has been found in Kyushu District of Japan and the breeding of grassy stunt has been especially severe in South west of Kyushu District though the breeding of grassy stunt has been found in only South East Asia. The diseased rice plants causes deterioration of quality of rice. The grassy stunt is serious disease in the torrid zone. The mediation of the virus is made by brown planthoppers which come from Southern zone to Japan in rainy season and seriously breed on rice in paddy field. The breeding of grassy stunt in Western District of Japan, especially Kyushu District, indicates the effect of disease in the Southern zone to Japan. The enlargement of the breeding of grassy stunt is anxiously considered. It is important to control brown planthopper in the zone for the breeding of the virus, as soon as possible.
Brown planthopper widely inhabits in paddy fields in Asia and come from such zone to Japan with South Western wet worm wind in rainy season. It is impossible to prevent invasion of the imago of brown planthopper. Therefore, it is difficult to prevent initial infection. In the South west of Kyushu District, it is important to reduce the initial infection. Moreover, it is necessary to effectively prevent secondary infection. It is necessary to control brown planthopper by pesticide. However, there are various problems because of lowering of sensitivity to insect pesticides.
The pyrethroid compounds used in the present invention have the formula ##STR2## wherein X represents hydrogen atom or ethynyl group. The pyrethroid compound (I) having ethynyl group as X is known as an insect pesticide which is effective to agricultural pests such as rice stem borer, smaller brown planthopper (Laodelphax striatellus), green rice leafhopper (Nephotettix cincticeps) (refer to Japanese Unexamined Patent Publication No. 33452/1980). The pyrethroid compound (I) having hydrogen atom as X is a novel compound which has insect pesticidal effect to green rice leafhopper (Nephotettix cincticeps), rice stem borer, tobacco cutworm, smaller brown planthopper (Laodelphax striatellus), etc. However, the pesticidal effect of these pyrethroid compound (I) to brown planthopper is not satisfactory. When the pyrethroid compound (I) is applied, the effect is not always stable. In the practical application, it is preferable to combine it with a synergistic active ingredient.
On the other hand, O,O-di-C.sub.2-3 alkyl S-benzyl- or S-halobenzyl-phosphorothiolates, especially O,O-diisopropyl S-benzylphosphorothiolate or O,O-diisopropyl S-halobenzyl-phosphorothiolate (hereinafter referred to as IBP) has excellent germicidal effect on agricultural germs for rice etc., however, does not have effective insect pesticidal effect on agricultural insect pests at a practical dose.